<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    #box{
      width: 100px;
      height: 100px;
      background: #000;
    }
  </style>
</head>
<body>
  <div id="box"></div>

  <script>
    // 创建一个支持冒泡且不能取消的look事件
    let ev = new Event('look', { bubbles: true, cancelable: false, composed: false })


    let box = document.getElementById("box");
    let boxShadow = box.attachShadow({ mode: 'open', delegatesFocus: false });
    boxShadow.innerHTML = `
      <div class="title">我是影子DOM</div>
    `


    box.addEventListener("look", (event) => {
      if (event.cancelable) {
        event.preventDefault()
      } else {
        console.log('在box上触发了look事件');
      }
    })

    let boxChild = box.shadowRoot.querySelector('.title')

    boxChild.dispatchEvent(ev)
  </script>
</body>
</html>